/***********************************************************
  说明:本程序用于演示ping命令的实现原理                   *
 ***********************************************************/
#include <stdio.h>
#include <signal.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>
#include <setjmp.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>


#define PACKET_SIZE     4096
#define MAX_WAIT_TIME   5
#define MAX_NO_PACKETS  3
char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];
int sockfd,datalen=56;
int nsend=0,nreceived=0;
struct sockaddr_in dest_addr;
pid_t pid;
struct sockaddr_in from;
struct timeval tvrecv;
void statistics(int signo);
unsigned short cal_chksum(unsigned short *addr,int len);
int pack(int pack_no);
void send_packet(void);
void recv_packet(void);
int unpack(char *buf,int len);
void tv_sub(struct timeval *out,struct timeval *in);

void statistics(int signo)
{       printf("\n--------------------PING statistics-------------------\n");
	printf("%d packets transmitted, %d received , %%%d lost\n",nsend,nreceived,
			(nsend-nreceived)/nsend*100);
	close(sockfd);
}
/*校验和算法*/
unsigned short cal_chksum(unsigned short *addr,int len)
{       int nleft=len;
	int sum=0;
	unsigned short *w=addr;
	unsigned short answer=0;

	/*把ICMP报头二进制数据以2字节为单位累加起来*/
	while(nleft>1)
	{       sum+=*w++;
		nleft-=2;
	}
	/*若ICMP报头为奇数个字节，会剩下最后一字节。把最后一个字节视为一个2字节数据的高字节，这个2字节数据的低字节为0，继续累加*/
	if( nleft==1)
	{       *(unsigned char *)(&answer)=*(unsigned char *)w;
		sum+=answer;
	}
	sum=(sum>>16)+(sum&0xffff);
	sum+=(sum>>16);
	answer=~sum;
	return answer;
}
/*设置ICMP报头*/
int pack(int pack_no)
{       int i,packsize;
	struct icmp *icmp;
	struct timeval *tval;
	icmp=(struct icmp*)sendpacket;
	icmp->icmp_type=ICMP_ECHO;
	icmp->icmp_code=0;
	icmp->icmp_cksum=0;
	icmp->icmp_seq=pack_no;
	icmp->icmp_id=pid;
	packsize=8+datalen;
	tval= (struct timeval *)icmp->icmp_data;
	gettimeofday(tval,NULL);    /*记录发送时间*/
	icmp->icmp_cksum=cal_chksum( (unsigned short *)icmp,packsize); /*校验算法*/
	return packsize;
}
/*发送三个ICMP报文*/
void send_packet()
{       int packetsize;
	while( nsend<MAX_NO_PACKETS)
	{       nsend++;
		packetsize=pack(nsend); /*设置ICMP报头*/
		if( sendto(sockfd,sendpacket,packetsize,0,
					(struct sockaddr *)&dest_addr,sizeof(dest_addr) )<0  )
		{       perror("sendto error");
			continue;
		}
		sleep(1); /*每隔一秒发送一个ICMP报文*/
	}
}
/*接收所有ICMP报文*/
void recv_packet()
{   
	int n,fromlen;
	extern int errno;
	int i=0;
	signal(SIGALRM,statistics);
	fromlen=sizeof(from);
	while( nreceived<nsend)
	{       alarm(MAX_WAIT_TIME);
		if( (n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),0,
						(struct sockaddr *)&from,&fromlen)) <0)
		{       if(errno==EINTR)continue;
			perror("recvfrom error");
			i++;
			if(i == 20)
			{
				break;
			}
			continue;
		}
		gettimeofday(&tvrecv,NULL);  /*记录接收时间*/
		if(unpack(recvpacket,n)==-1)continue;
		nreceived++;
	}
}
/*剥去ICMP报头*/
int unpack(char *buf,int len)
{       int i,iphdrlen;
	struct ip *ip;
	struct icmp *icmp;
	struct timeval *tvsend;
	double rtt;
	ip=(struct ip *)buf;
	iphdrlen=ip->ip_hl<<2;    /*求ip报头长度,即ip报头的长度标志乘4*/
	icmp=(struct icmp *)(buf+iphdrlen);  /*越过ip报头,指向ICMP报头*/
	len-=iphdrlen;            /*ICMP报头及ICMP数据报的总长度*/
	if( len<8)                /*小于ICMP报头长度则不合理*/
	{       printf("ICMP packets\'s length is less than 8\n");
		return -1;
	}
	/*确保所接收的是我所发的的ICMP的回应*/
	if( (icmp->icmp_type==ICMP_ECHOREPLY) && (icmp->icmp_id==pid) )
	{       tvsend=(struct timeval *)icmp->icmp_data;
		tv_sub(&tvrecv,tvsend);  /*接收和发送的时间差*/
		rtt=tvrecv.tv_sec*1000+tvrecv.tv_usec/1000;  /*以毫秒为单位计算rtt*/
		/*显示相关信息*/
		printf("%d byte from %s: icmp_seq=%u ttl=%d rtt=%.3f ms\n",
				len,
				inet_ntoa(from.sin_addr),
				icmp->icmp_seq,
				ip->ip_ttl,
				rtt);
	}
	else    return -1;
}
int test_network(char *argv)
{
        struct hostent *host;
	struct protoent *protocol;
	unsigned long inaddr=0l;
	int waittime=MAX_WAIT_TIME;
	int size=50*1024;
	if( (protocol=getprotobyname("icmp") )==NULL)
	{       perror("getprotobyname");
		exit(1);
	}
	/*生成使用ICMP的原始套接字,这种套接字只有root才能生成*/
	if( (sockfd=socket(AF_INET,SOCK_RAW,protocol->p_proto) )<0)
	{       perror("socket error");
		exit(1);
	}
	/* 回收root权限,设置当前用户权限*/
	setuid(getuid());
	/*扩大套接字接收缓冲区到50K这样做主要为了减小接收缓冲区溢出的
	  的可能性,若无意中ping一个广播地址或多播地址,将会引来大量应答*/
	setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size) );
	bzero(&dest_addr,sizeof(dest_addr));
	dest_addr.sin_family=AF_INET;
	/*判断是主机名还是ip地址*/
	inaddr = inet_addr(argv);
	if( inaddr == INADDR_NONE)
	{       if((host=gethostbyname(argv) )==NULL) /*是主机名*/
			{
				perror("gethostbyname error");
				return -1;
			}
		memcpy( (char *)&dest_addr.sin_addr,host->h_addr,host->h_length);
	}
	else    /*是ip地址*/
	{
		memcpy( (char *)&dest_addr.sin_addr,(char *)&inaddr,sizeof(inaddr));
	}
	/*获取main的进程id,用于设置ICMP的标志符*/
	pid=getpid();
	printf("PING %s(%s): %d bytes data in ICMP packets.\n",argv,inet_ntoa(dest_addr.sin_addr),datalen);
	send_packet();  /*发送所有ICMP报文*/
	recv_packet();  /*接收所有ICMP报文*/
	statistics(SIGALRM); /*进行统计*/
	if(nreceived < 1)
	{
		printf("the network is not get\n");
		return -1;
	}
	else
	{
		printf("the network is get\n");
		return 0;
	}
}
/*两个timeval结构相减*/
	void tv_sub(struct timeval *out,struct timeval *in)
{       if( (out->tv_usec-=in->tv_usec)<0)
	{       --out->tv_sec;
		out->tv_usec+=1000000;
	}
	out->tv_sec-=in->tv_sec;
}
/*------------- The End -----------*/
